If you generally like the Axiom sound but are looking to upgrade, you should start with other "Canadian" manufacturers. PSB and Paradigm are often considered an upgrade to Axiom. (I am an Axiom fan, have the M22s, so that should not be considered a criticism of Axiom.)

Yes, the center should absolutely match the left/right (called timbre matched), so that as a scene pans from side to side you don't get an abrupt change. It's not as important for surrounds, so you could keep the QS4s in place until you settle in on the mains.

By the way, if you have old Axioms, the version changes from v1 to v2 to v3 were supposed to be a significant upgrade in the crossover and tweeters; so if all else fails you could try out the newer models.

I have a pair of Image T6 mains and a C5 center and love them for both movies and music. I've had them for a number of years and they aren't going anywhere. I also have a pair of the Image S5 Bipoles for surrounds and a pair of ancient Alphas for my rear surrounds to round out the "7" in my 7.1 setup.

The Alphas are the last remnants of my first set of home theater speakers - 4 alphas and a matching center. They were solid performers for $100 bookshelves back in the day...

My subwoofer is a Paradigm 15"-er - got it through a friend at a great discount. It's more subwoofer than I think I'll ever need for my room.